Gamma Distribution problem

In a certain country, the distribution of incomes in thousands of dollars is described by a gamma distribution with [itex]\alpha[/itex] = 2 and [itex]\beta[/itex] = 8. What is the probability that a man chosen at random will have the following incomes?

a. More than $14,000
b. At least $12,000

So I know that f(x;[itex]\alpha[/itex],[itex]\beta[/itex]) = [itex]\frac{1}{\Gamma(\alpha)\beta^{\alpha}}[/itex]x[itex]^{\alpha-1}[/itex]e[itex]^{-x/\beta}[/itex] for x>0,[itex]\alpha[/itex],[itex]\beta[/itex]>0